WiFi DAS

Wireless carriers are always looking for ways to offload their data traffic because it relieves their capacity problem. However, WiFi has been treated by wireless carriers as something to always be cautious of. This is for several reasons. First, carriers don’t have an easy means of monetizing such services. Customers from a particular carrier expect to use their WiFi service free-of-charge wherever it’s available. Security is also a concern. It’s much easier to tamper with access points and intercept WiFi traffic than a carrier BTS at a relatively secure location. Carriers are weary of their customers jumping on 3rd party WiFi networks, only to experience connection issues. Most customers cannot distinguish between carrier LTE and WiFi networks and will start complaining when their music streaming inexplicably stops.

WiFi DAS is not common terminology, because multi-carrier cellular DAS systems don’t carry WiFi signals. WiFi networks always run separately and are mostly handled by IT professionals rather than DAS integrators. Typical WiFi networks involve deploying commercial grade access points (AP) built by manufacturers such as Cisco or Aruba Networks. These AP employ dual frequencies at 2.4 and 5 GHz. Also, smart antenna technology known as Multiple-In-Multiple-Out (MIMO) is integrated into the latest AP. We won’t describe the exact RF characteristics or functions of MIMO as they are beyond the scope of this publication. Briefly though, MIMO utilizes more than 1 antenna (usually 2) to improve performance and data throughput. Somebody figured out its better to use multiple antennas than increasing the transmit power of a single antenna.

Typical WiFi installations involve multiple AP placed throughout a venue depending on the size of the area and the number of users supported. These AP are usually connected via Ethernet cable know as RJ-45 and powered over Ethernet as well. AP controller devices located at a Head-End location select appropriate channels and allocate network capacity. Everything is software controlled and the interface is GUI driven which is accessible remotely via browser or your local access network (LAN). The AP controller is connected to an IP network.

There are companies in the US like Boingo Wireless who have managed to monetize WiFi services. They provide paid subscription and free advertisement-supported services. You will find such services mostly at airports, hotels and retail locations like malls. Wireless carriers are taking notice. Soon you will start seeing collaboration between carriers and WiFi service providers like Boingo where wireless traffic offload occurs. From the customers’ perspective, everything has to be seamless. Network capacity and data throughput over WiFi networks will dictate the outcome. If you’ve ever tried jumping on the WiFi network of any major airport, you know they have a long ways to go. The problem will become more evident as wireless carriers begin deploying a new technology called Voice over LTE (VoLTE).

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2 Comments

jim warner
on December 18, 2014 at 12:32 am

WiFi AP controllers can be located anywhere. They do not need to be at the head-end. In fact, WiFi generally doesn’t have a head-end. The article offers to explain WiFi DAS. But somehow it never gets around to doing that.

Cisco takes a dim view of attempting to run their WiFi over a distributed antenna system. They come just about as close as you can to saying “don’t do it” without actually saying it. A copy of their position paper on the topic is at:

I think that rather than collaboration between carriers and Boingo et. al., you can expect the carriers to move in to the 5 GHz wifi band with LTE-U. The “U” stands for unlicensed. This is an initiative being lead by Qualcom.

-jim warner
University California Santa Cruz

Bob Fay
on December 19, 2014 at 4:36 am

This article fails to explain that these active AP’s are not distributing the same RF signal or capacity instead they are typically deployed similar to a cellular system where each AP provides a limited amount of the overall coverage and capacity employing a frequency reuse scheme in which the adjacent AP’s employ disparate RF channels to prevent interference while allowing the reuse of an RF channe any wherever it will not abut the coverage provided by another AP employing the same RF channel thereby providing expanded coverage and capacity through the deployment of multiple disparate AP’s like a pico-cell system deployment.
Conversely, a DAS system provides enhanced/expanded coverage by distributing the same signal(s) either passively over coax or actively over a combination of fiber and coax to multiple antennae strategically locate passed on engineered designs without any increase in capacity.
Current DAS systems lack the ability to distribute disparate RF signals to the granularity required to support the architecture of a distributed Wi-Fi deployment and without that ability a DAS system would only be able to enhance or expand the coverage of a single AP which unlike a BDA or BTS would be very limited making it unwise.